In today's society, paper, plastics, aluminum foils and the like have been used widely as packaging materials of various foods, medicines, sundry goods and the like in the form of liquid, powder or solid, agricultural materials and building materials. In particular, plastics have been used in many applications such as bags and containers owing to their excellent strength, water resistance, moldability or formability, transparency, cost and the like. Plastics used for such applications now are, for example, polyethylene, polypropylene, polystyrene, polyvinyl chloride and polyethylene terephthalate. However, molded products made of these plastics are neither biodegraded nor hydrolyzed under natural environments, or have their markedly low decomposition rate, they may remain in the soil when buried therein or spoil a view when discarded after use. Even if they are incinerated, they may pose a problem such as emission of a harmful gas or damage to the incinerator.
A number of researches have been carried out on materials that are biodegradable into a carbon dioxide gas and water by microorganisms in the soil or water as a means for solving the above-described problems. Typical examples of the biodegradable materials include aliphatic polyester resins such as polylactic acid, polybutylene succinate, and polybutylene succinate adipate and aromatic-aliphatic copolymer polyester resins such as polybutylene adipate terephthalate.
Of these, polylactic acid is one of the most typical polyesters but for it, an extremely low biodegradation rate is a big problem (Non-patent Document 1). Polybutylene succinate, polybutylene succinate adipate and the like having similar mechanical properties to those of polyethylene are, on the other hand, aliphatic polyesters having a relatively high biodegradation rate. They are advantageous in that molded products of them after use can be easily biodegraded or they easily compost. Their biodegradation rate is however not sufficiently high and a means for controlling their rate has not yet been developed.
Such polyesters are now produced by making use of polycondensation of raw materials derived from fossil fuel resources. In view of concerns about depletion of fossil fuel resources or an increase in carbon dioxide in the air that poses a global-scale environmental problem in recent years, methods for producing raw materials of these polymers from biomass resources have attracted attentions. Since these resources are renewable carbon-neutral biomasses, such methods are expected to gain in particular importance in future.
There have heretofore been developed technologies for preparing a dicarboxylic acid such as succinic acid or adipic acid from glucose, dextrose, cellulose, or oil or fat derived from biomass resources by using the fermentation process (refer to Patent Document 1, Non-patent Documents 1, 2 and 3).
These processes however provide a target dicarboxylic acid by preparing an organic acid salt of the dicarboxylic acid through fermentation and then subjecting it to steps such as neutralization, extraction and crystallization. Many impurities such as nitrogen elements derived from fermentation microorganisms, ammonia and metal cations, as well as nitrogen elements contained in the biomass resources, are therefore mixed in the dicarboxylic acid inevitably.
There is also disclosed a production process of a biomass-resource-derived polyester (Patent Document 2).
Non-Patent Document; Expected Materials on the Future, Vol. 1, No. 11, p 31 (2001)
Patent Document 1: Japanese Patent Laid-Open No. 2005-27533
Non-Patent Document 2: Biotechnology and Bioengineering Symp. No. 17 (1986), 355-363
Non-Patent Document 3: Journal of the American Chemical Society No. 116 (1994), 399-400
Non-Patent Document 4: Appl. Microbiol. Biotechnol No. 51 (1999), 545-552
Patent Document 2: Japanese Patent Laid-Open No. 2005-139287